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you do not need to add any material for welding, you have a couple options you can either add the weld in the 3D which is a representation of the weld and you can import that into your drawing or you can simply add a weld symbol to your part drawing calling out the weld type.
See the attached video on how to add a weld in the 3D environment
and Here for adding a weld symbol on a drawing
WeldBead.mp4 1.5 MB
In pre 2015 versions, this is almost impossible, because you are trying to weld a face to itself. If you have an academic version, it is likely 1-2 years behind the year it claims to be. You can try splitting the face on the back of the cylinder--but I don't have an old version to test this on.
Newer versions have options to define weld bead paths that make it easier.